Does anyone know anything about regelation?

Question

I'm can't really find anything on it. I know that it is the process by which ice melts under pressure. Why does it?

Answer 1

If you examine a phase diagram of water, you will see that the line dividing the solid (ice) and liquid phases is negatively-sloped.

This means if water is at 1 atmosphere of pressure and -1 degrees Celsius, you will notice that it is ice. However, if the temperature stays the same, but the pressure increases dramatically, the phase diagram points to the favored form being liquid water. The steep slope of this line means that it takes a large increase in pressure to liquefy the ice, but only a small decrease in temperature to re-freeze it.

Most materials do not have this negatively-sloped line. The reason water does is that solid water (ice) is less dense than liquid water, a relatively rare phenomenon among chemicals. When you increase pressure, a substance will tend try to revert to a denser to become smaller and 'relieve' the pressure. With most substances, the denser form is a solid. For example, increasing pressure on carbon dioxide will eventually cause it to solidify. Water is peculiar, however, and will respond in the opposite fashion, because the liquid form is denser than the solid form.